The invention concerns a procedure for automatic particle size analysis of particle mixtures, specifically with respect to influencing the technical control of producing and processing such mixture.
The determination of particle size distribution of a disperse mixture shall, as a rule, be done quickly and be representative of an overall aggregate. Aside from the known procedures, such as screen analysis and sedimentation, the opto-electronic measuring procedures are gaining more and more importance, since they primarily satisfy requirements concerning automatization capability.
In Patent Specifications DD-WP 260 764 and DD-WP 278 859, procedures are described for the determination of the granulometric condition and/or granulation ratio of grain mixtures, from which a sample is continuously or also intermittently drawn, and where the particles are optically separated and moved, at predetermined, uniform velocity, at right angles, past a CCD line sensor.
In DD-260-764, the particles are scanned, line by line, in chronologically constant succession. The thus signaled widths of the respective particle segments (chords) are classified into categories of different chord lengths. When reaching a set meter number or meter time, the so-called granulation number is ascertained via a calibration function. Involved here is a rapid procedure, by which for each picked-up particle several chord lengths are recorded and included in the evaluation.
With respect to mixtures of narrowly restricted particle sizes, however, this procedure is unsuitable, inasmuch as the selectivity of the calibration function is no longer adequate.
The practical drawbacks of both inventions consist in the requirement for uniform particle velocity during the measuring process. Such condition either requires high technical expenditure, for instance a vacuum measuring cell, or it restricts the measuring area by neglecting the friction, which is admissible only with relatively heavy particles.
The procedure according to DD-WP 260 764 functions only with nearly similar distribution functions and does not provide any information concerning the course of the particle size distribution. Patent specification DD-WP 278-859 requires that each particle is scanned at least once. This results in an extremely high rate of data, which leads to technical measuring problems or which only permits very low throughput of material under test, which prevents on-line operation.
Procedures which are oriented toward more precise evaluation, are based in that static images are produced via opto-electronic devices, which are then evaluated by means of additional costly device elements or mathematical methods.
From DE-PS 2855 583, a procedure is known whereby a sample of a particle mixture drops from an appropriate height and pictures of the particles are recorded during the dropping with a television camera. From the individual, successively projected static images, the surface distribution of the mixture is ascertained on the basis of the measured projection surfaces. Long measuring times preclude wide application.